Systems in which a terminal device connected to a server uses functions provided by the server to process data are known from the literature (see, for example, PTL 1). A problem with such systems is that the system stops working if the communication path connecting the server and the terminal device is interrupted. To handle this problem, the POS (point-of-sale) system described in PTL 1 has an auxiliary server device with a line confirmation device between the server and the client. The system in PTL 1 connects the auxiliary server device and the server through two Internet connections, and when communication through one Internet connection cannot be confirmed, the client and server communicate through the other Internet connection.